Epilepsy-Specific Citation Classics Revisited
In Clinical Science With the exponential increase in peer-reviewed medical literature in recent decades, it is difficult to stay current in a field of expertise and easy to miss important articles. It is particularly challenging for those new to a field to become familiar with the existing body of scientific literature-the foundation on which future research and clinical paradigms are built. Given the large number of papers, evolving terminology and knowledge, and multidisciplinary nature of
... field of epilepsy, it would be ideal to create a curriculum or reading list for trainees and new researchers. Citation frequency is one of several indicators that can be used to identify seminal articles that have had a significant scientific impact. The term "citation classic" was originally coined in a 1987 article in JAMA that identified and analyzed JAMA's 100 most-cited articles in its history (1). Since that time, there have been numerous articles in a variety of fields that use bibliometrics to identify and analyze the most cited literature. The purpose of this review is to identify and highlight "citation classics" in the epilepsy and seizure literature, defined as articles that have been cumulatively cited over 400 times. This review serves as a 5-year update to a 2012 article by Ibrahim et al. as published in Epilepsia (2). Our goals were to: 1) identify the most-cited articles relevant to epilepsy, which theoretically have had the highest impact; and 2) analyze trends in the literature that can indicate future directions of research. Methods To identify epilepsy-specific citation classics, we queried Scopus, the largest abstract and citation database of peerreviewed literature, which includes scientific journal articles, books, and conference proceedings. Scopus was searched for all English language publications using the terms "epilep*" (inclusive of epilepsy, epileptic, epilepsies, and epilepticus) or "seizure*" (inclusive of seizure or seizures) in the title, abstract, or keywords. As in Ibrahim et al. (2), articles cited fewer than 400 times as sources in others' works were excluded from review. Two board-certified epileptologists (MK and DS) independently reviewed the title and abstract of each publication to determine if it was an epilepsy-specific or seizure-specific article, meaning that epilepsy or seizures were a central topic of study, discussion, or investigation. If there was any ambiguity or disagreement about the appropriateness of inclusion of an article, a third epileptologist and basic science researcher (GW) performed an independent review and contributed to the consensus decision. For example, a heavily cited review on multiple sclerosis mentioned rates of seizures in the MS population, but the article was excluded because it was not epilepsy specific; likewise, a review article entitled "Glutamate Uptake" was excluded because epilepsy and seizures were not the central theme of the review, despite discussion of certain antiepileptic drug (AED) mechanisms. Papers that discussed specific disease conditions or states were included if epilepsy was a central manifestation of the disease (e.g., Rasmussen syndrome, myoclonic epilepsy with ragged red fibers [MERRF] or NMDA receptor antibody encephalitis). Articles addressing mechanisms or efficacy of AEDs were also included. The resulting citation classics were grouped into three broad categories: 1) human research, 2) animal research, and 3) reviews, guidelines, classification schemes, or consensus statements. This grouping differs slightly from that of Ibrahim et al., who defined the categories as 1) laboratory investigations, 2) clinical research, or 3) reviews or classification studies (2). We modified the categories because translational human research has been increasingly lab-based, particularly in genetics and neuroimmunology. As a check on our methodology, we ran a similar search strategy in Harzing's Publish or Perish (HPP) on April 5, 2017, the search method used by Ibrahim et al. HPP is an internet-based search engine that uses Google Scholar and Microsoft Academic data to calculate its citation metrics. Finally, a qualitative analysis of the evolution of citation classics was undertaken, focusing on hot topics and methods by category over each decade. Due to the broad scope and frequent cross-disciplinary nature of epilepsy and seizure research-as well as incomplete key word indexing (especially for earlier studies)-a quantitative analysis of categories was not feasible. Pearson correlation coefficients were calculated to look for potential correlations between bibliometric "journal impact" scores (Scopus journal metrics, SJR, and CiteScore; 3) and number of publications or average citations per journal.